The invention relates to a method of forming a signal entered into a multistage amplifier, into a desired pulse contour or spectrum.
German Patent Document DE 29 04 011 C3 discloses a high-frequency amplifier which includes series-connected power transistor amplifier stages 22, 23, 24 constructed in a common base circuit, as illustrated in FIG. 1. High-frequency pulses Son entered through an input adaptation network are amplified on the emitter side and are output on the collector side via an output adaptation network Soff, with the pulses having a defined envelope form. A constant current source 25, 26, 27 controlled by a pulse generator 10 is connected to each amplifier stage 22, 23, 24, and impresses a current corresponding to the course of the pulse onto the collector-emitter path of the respective power transistor 22, 23, 24 for the duration of each pulse 29 emitted by the pulse generator 10.
This circuit has the disadvantage, however, that interactions between the individual stages may occur during the simultaneous switching-on or switching-off of the amplifier stages, because each power transistor exhibits a different transient response. Such interactions may lead to undesirable spectral fractions.